Virtual oscilloscope components
Features of virtual oscilloscope
The currently widely used USB interface is used to make the interface between virtual instruments and computers more convenient and the communication speed is higher; a high-speed analog-to-digital conversion chip (ADC) is used for high-speed sampling; a high-performance microcontroller is used for control, and a high-speed large-capacity memory (RAM ) Saves sampling data in real time, improving the performance of the instrument; using Labview language to design a host computer application, which can realize waveform display, as well as data analysis and processing.
Components of a Virtual Oscilloscope
(1) Signal acquisition and control. It is a hardware platform composed of computers and instrument hardware to realize the collection, measurement, conversion and control of signals.
(2) Data analysis and processing. The virtual oscilloscope makes full use of the storage and computing functions of the computer, and analyzes and processes the input data signals through software. Processing content includes digital filtering, data statistics, numerical analysis, etc. From the perspective of data analysis, virtual oscilloscopes have more powerful data analysis capabilities than traditional instruments.
(3) Display of measurement results. The virtual oscilloscope makes full use of computer resources, such as displays, memories, etc., to express and output measurement results in a variety of ways. Its output forms include long-distance data transmission through the bus network, copy output through optical disks and disks, and output on the hard disk. A method of storing data and outputting it through a graphical interface such as a computer screen.
Technical parameters of virtual oscilloscope
Issues that should be paid attention to when using virtual oscilloscope
Distinguish between analog bandwidth and digital real-time bandwidth
Bandwidth is one of the most important specifications of an oscilloscope. The bandwidth is a fixed value, while the bandwidth of the virtual oscilloscope has two types: analog bandwidth and digital real-time bandwidth. The highest bandwidth that a virtual oscilloscope can achieve by using sequential sampling or random sampling technology for repetitive signals is the digital real-time bandwidth of the oscilloscope. The digital real-time bandwidth is related to the highest digitization frequency and the waveform reconstruction technology factor K (digital real-time bandwidth = highest digitization rate/K) , is generally not given directly as an indicator. It can be seen from the definitions of the two bandwidths that the analog bandwidth is only suitable for the measurement of repetitive periodic signals, while the digital real-time bandwidth is suitable for the measurement of both repetitive signals and single signals. The manufacturer claims that the bandwidth of the oscilloscope can reach several megabytes, but it actually refers to the analog bandwidth. The digital real-time bandwidth is lower than this value. For example, the bandwidth of TEK's TES520B is 500MHz, which actually means that its analog bandwidth is 500MHz, while the highest digital real-time bandwidth can only reach 400MHz, which is far lower than the analog bandwidth. Therefore, when measuring a single signal, you must refer to the digital real-time bandwidth of the virtual oscilloscope, otherwise it will bring unexpected errors to the measurement.
About the sampling rate: The sampling rate is also called the digitization rate, which refers to the number of samples of the analog input signal per unit time, often expressed in MS/s. Sampling rate is an important specification of a virtual oscilloscope. If the sampling rate is not enough, aliasing may easily occur
If the input signal of the oscilloscope is a 100KHz sine signal, but the signal frequency displayed by the oscilloscope is 50KHz, this is because the sampling rate of the oscilloscope is too slow, resulting in aliasing. Aliasing is when the frequency of the waveform displayed on the screen is lower than the actual frequency of the signal, or the displayed waveform is unstable even though the trigger on the oscilloscope is lit. The generation of aliasing is shown in Figure 1. Then, for a waveform of unknown frequency, you can judge whether the displayed waveform has aliased like this: slowly change the sweep speed t/div to a faster time base file, and see if the frequency parameters of the waveform change sharply. If so, It means that waveform aliasing has occurred; or the shaking waveform has stabilized at a faster time base, which also means that waveform aliasing has occurred. According to the Nyquist theorem, the sampling rate must be at least twice higher than the high-frequency component of the signal to prevent aliasing. For example, a 500MHz signal requires a sampling rate of at least 1GS/s. There are several ways to simply prevent aliasing from happening:
?Use automatic settings
?Adjust scanning speed;
?Try to switch the collection mode to envelope mode or peak detection mode, because envelope mode is to find extreme values in multiple collection records, while peak detection mode is to find the maximum and minimum values in a single collection record. Both methods can detect faster signal changes.
